Biomedical subjects

K D Craven

Publications and source records attributed to K D Craven.

7 recordsLinked to original sources

PubMed2004

Prevalence of interspecific hybrids amongst asexual fungal endophytes of grasses.

Epichloë endophytes are fungal symbionts of grasses that span a continuum including asexual mutualists that are vertically transmitted, obligately sexual pathogens that are horizontally transmitted, and mixed-strategy symbionts with both mutualistic and pathogenic capabilities. Here we show that processes of genome evolution differ markedly for the different symbiont types. Genetic and phylogenetic analysis was conducted of a broad taxonomic, ecological and geographical sample of sexual and asexual isolates, in which were identified and sequenced alleles of genes for beta-tubulin (tub2) and translation elongation factor 1-alpha (tef1), and microsatellite alleles were identified by length polymorphisms. The majority of asexual isolates had two or three alleles of most loci, but every sexual isolate had only single alleles for each locus. Phylogenetic analysis of tub2 and tef1 indicated that in all instances of multiple alleles in an isolate, the alleles were derived from different sexual species. It is concluded that, whereas horizontally transmissible species had haploid genomes and speciation occurred cladistically, most of the strictly seedborne mutualists were interspecific hybrids with heteroploid (aneuploid or polyploid) genomes. Furthermore, the phylogenetic evidence indicated that, in at least some instances, hybridization followed rather than caused evolution of the strictly seedborne habit. Therefore, the abundance of hybrid species among grass endophytes, and their prevalence in many host populations suggests a selective advantage of hybridization for the mutualistic endophytes.

Base Sequence↗

PubMed2003

Interspecific hybridization in plant-associated fungi and oomycetes: a review.

Fungi (kingdom Mycota) and oomycetes (kingdom Stramenopila, phylum Oomycota) are crucially important in the nutrient cycles of the world. Their interactions with plants sometimes benefit and sometimes act to the detriment of humans. Many fungi establish ecologically vital mutualisms, such as in mycorrhizal fungi that enhance nutrient acquisition, and endophytes that combat insects and other herbivores. Other fungi and many oomycetes are plant pathogens that devastate natural and agricultural populations of plant species. Studies of fungal and oomycete evolution were extraordinarily difficult until the advent of molecular phylogenetics. Over the past decade, researchers applying these new tools to fungi and oomycetes have made astounding new discoveries, among which is the potential for interspecific hybridization. Consequences of hybridization among pathogens include adaptation to new niches such as new host species, and increased or decreased virulence. Hybrid mutualists may also be better adapted to new hosts and can provide greater or more diverse benefits to host plants.

Adaptation, Biological↗

PubMed1994

Unfit drivers.

Explore the source record for details and available documents.

Automobile Driver Examination↗

PubMed1981

Extrapericardial and esophageal pressures with positive end-expiratory pressure in dogs.

Using flat balloon techniques to minimize distortion and artifacts, we studied the effect of positive end-expiratory pressure (PEEP) on local surface pressures between the lung and pericardium overlying the right (R) and left (L) ventricles of ventilated closed-chest anesthetized dogs in right lateral decubitus position. To test the hypothesis that local extrapericardial [Pep(L) and Pep(R)] and average pleural pressures change equally with PEEP, we also measured esophageal pressure (Pes). When 10-cmH2O PEEP was applied, mean increases in Pes, Pep(L), and Pep(R) were 6.2, 5.6, and 5.3 cmH2O, respectively. When PEEP was raised to 20 cmH2O, further average increases in Pes, Pep(L), and Pep(R) were 5.8, 5.0, and 5.4 cmH2O. At each level of PEEP, volume infusion was used to increase stroke volume. Volume infusion at 20-cmH2O PEEP was associated with small 1.0- and 1.5-cmH2O increases in Pep but no change in Pes. Analysis of confidence limits showed that application of up to 20-cmH2O PEEP, with or without volume infusion to restore stroke volume, is associated with nearly equal changes in esophageal and local extrapericardial pressures.

Animals↗

PubMed1979

Pathophysiology of pulmonary contusion in dogs.

We produced a localized right lower lobe (RLL) contusion in 14 anesthetized ventilated dogs, 7 of which were treated with positive end-expiratory pressure (PEEP group). We measured gas exchange, pulmonary mechanics, and regional function before and 5 h after the contusion. Arterial PO2 decreased by 20 Torr and venous admixture doubled in both groups during air breathing. The shunt fraction (Qs/Qt) was minimally increased, despite a large lobar Qs/Qt (0.43) in the contused RLL. These results were explained by reduced ventilation per unit volume (VA/V), and ventilation-to-perfusion ratios of the contused RLL measured with 133Xe technique. We conclude that pulmonary contusion causes a leak of blood and plasma, flooding 25% of the air spaces of the RLL at FRC, reducing the compliance of adjacent air spaces, and resulting in a reduced VA/V and a large RLL Qs/Qt. These results are consistent with the observed reduction in regional volume and perfusion in the contused RLL, and suggest that Qs/Qt was not increased because blood flow was markedly reduced to flooded air spaces. PEEP reduced the hypoxemia, but increased the contusion.

Animals↗

PubMed1979

Effects of contusion and flail chest on pulmonary perfusion and oxygen exchange.

Localized pulmonary contusions were produced in the right lower lobes (RLL) of 12 anesthetized ventilated dogs, 6 of which had a flail segment in the chest wall over the RLL. Pulmonary oxygen exchange during ventilation with air and oxygen, and the lobar distribution of pulmonary perfusion by radioactive microsphere techniques were measured before and 3 h after contusion, and again after thoracotomy. These were compared to 12 noncontused dogs, 6 of which had a flail segment. Contusion produced an average decrease of 20 Torr in Pao2 during air breathing and an average increase in Qs/Qt of less than 5%, surprisingly small given the doubled weight and average 44% shunt calculated in the contused lobe after thoracotomy. No significant effect of flail or thoracotomy was found, indicating that the presence of an intact chest wall and lung-chest wall interdependence was not a major factor preventing a larger increase in intact whole-animal shunt of contused dogs. Rather, the small effect of this severe lobar injury on whole-animal shunt was due to a 30% decrease in RLL relative perfusion. This reduction was demonstrated to be localized to a smaller hemorrhagic subsection of the contused lobe.

Animals↗

PubMedDate not supplied

Molecular identification of the turf grass rapid blight pathogen.

Rapid blight is a newly described disease on turf grasses, primarily found on golf courses using suboptimal water for irrigation purposes. On the basis of shared morphological characteristics, it has been proposed that the rapid blight pathogen belongs to a genus of stramenopiles, Labyrinthula, which had been known to cause disease of marine plants only. We have collected 10 isolates from four species of turf grass in five states and sequenced portions of the SSU (18S) rDNA gene from each to provide a definitive taxonomic placement for rapid blight pathogens. We also included sequences from Labyrinthuloides yorkensis, Schizochytrium aggregatum, Aplanochytrium sp., Thraustochytrium striatum, Achlya bisexualis and several nonturf-grass isolates of Labyrinthula. We found that rapid blight isolates indeed are placed firmly within the genus Labyrinthula and that they lack detectable genetic diversity in the 18S rDNA region. We propose that the rapid blight pathogens share a recent common ancestor and might have originated from a single, infected population.

Genes, rRNA↗